GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with accelerator pedal position (APP) and engine speed. The engine control module (ECM) uses this information to assist in diagnosis of the barometric pressure (BARO) sensor and to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. If the ECM detects a boost sensor signal voltage that is excessively low, this DTC will set.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The boost pressure is less than 38 kPa for 2 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
    • The ECM limits fuel delivery.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. The boost sensor 5-volt reference circuit is shared with other sensors. If DTC P1639 is set, this indicates that the 5-volt reference circuit is shorted to ground and should be diagnosed first. The short may be on another sensor 5-volt reference circuit.

  2. Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Install a scan tool.
  2. Start the engine.
  3. Monitor the diagnostic trouble code (DTC) information with a scan tool.

Does the scan tool indicate that DTC P1639 is current?

--

Go to DTC P1639

Go to Step 3

3

Observe the boost sensor pressure with a scan tool.

Does the scan tool indicate that the pressure is less than the specified value?

38 kPa

Go to Step 5

Go to Step 4

4

  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 5

Go to Intermittent Conditions

5

  1. Turn OFF the ignition.
  2. Disconnect the boost sensor electrical connector. Refer to Boost Sensor Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp to a good ground.
  5. Probe the 5-volt reference circuit of the boost sensor with a test lamp.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 7

6

Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the boost sensor and the signal circuit of the boost sensor.

Does the scan tool indicate that the pressure is more than the specified value?

254 kPa

Go to Step 9

Go to Step 8

7

Test the 5-volt reference circuit of the boost sensor for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

8

Test the signal circuit of the boost sensor for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

9

Inspect for poor connections at the boost sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

10

Inspect for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Replace the boost sensor. Refer to Boost Sensor Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 13

--

13

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 14

Go to Step 2

14

Observe the stored information, Capture Info., with a scan tool.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK